Controller, control method, and program

ABSTRACT

A controller according to the present disclosure includes a whole-slip detecting unit ( 210 ) that detects, based on pressure information sent from a plurality of regions having different slipping characteristics when an object in contact with the plurality of regions is slipping, a state of a whole slip in which the object is slipping on each of the plurality of regions. An occurrence timing of the whole slip is different for each of the plurality of regions, and thus a state of a partial slip in which a part of the object is slipping is able to be detected, so that it is possible to detect a slip of the object with high accuracy.

FIELD

The present disclosure relates to a controller, a control method, and aprogram.

BACKGROUND

Conventionally, the following Patent Literature 1 discloses that whetheror not a slip has occurred on a contact surface is determined on thebasis of (i) a change amount in a center position of the pressureagainst the contact surface and (ii) gripping force of a gripping unitthat grips a target object body.

CITATION LIST Patent Literature

Patent Literature 1: JP 2008-055540 A

SUMMARY Technical Problem

Detection of a partial slip is effective in a case where a robot or thelike grips an object. The partial slip is a phenomenon that occursbefore a whole slip in which a relative position with respect to anobject deviates and the object slips off, and in which a part of acontact surface starts to slip. In this case, in a state of the partialslip, a deviation of a relative position with respect to an object doesnot occur.

However, a technology disclosed in the above-mentioned Patent Literature1 employs a method for detecting a whole slip when an object starts toslip, so that a gripping force is not able to be controlled unless theobject starts to slip. Thus, in the technology disclosed in theabove-mentioned Patent Literature 1, it is difficult to control agripping force before an object starts to slip so as to perform a stablegrip. Moreover, in the first place, the fact is that there presents noeffective technology for detecting a partial slip. When a partial slipis to be detected, shear deformation of a contact part which occursbefore a partial slip is detected, and thus it is difficult to decidethe minimum gripping force on the basis of the partial slip. Moreover,in a case where pressure distribution is uniform, for example, when anobject is hard or when an object surface is plane, progress of a partialslip is rapid, so that detection of the partial slip becomes difficult.

Thus, it has been desired to detect a slip of an object with highaccuracy by detecting a partial slip.

Solution to Problem

According to the present disclosure, a controller is provided thatincludes: a whole-slip detecting unit that detects, based on pressureinformation sent from a plurality of regions having different slippingcharacteristics when an object in contact with the plurality of regionsis slipping, a state of a whole slip in which the object is slipping oneach of the plurality of regions.

Moreover, according to the present disclosure, a control method isprovided that includes: based on pressure information sent from aplurality of regions having different slipping characteristics when anobject in contact with the plurality of regions is slipping, detecting astate of a whole slip in which the object is slipping on each of theplurality of regions.

Moreover, according to the present disclosure, a program is providedthat allows a computer to function as: a means for detecting, based onpressure information sent from a plurality of regions having differentslipping characteristics when an object in contact with the plurality ofregions is slipping, a state of a whole slip in which the object isslipping on each of the plurality of regions.

Advantageous Effects of Invention

As described above, according to the present disclosure, it is possibleto detect a slip of an object with high accuracy by detecting a partialslip.

The above-described effects are not necessarily limited, and any effectsindicated in the present specification or other effects that can beunderstood from the present specification may be exerted together withor instead of the above-described effects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a hand of a robotaccording to one embodiment of the present disclosure.

FIG. 2 is a diagram illustrating a state in which first and secondflexible layers are in contact with an object.

FIG. 3A is a diagram schematically illustrating chronological change ina contact state between a flexible layer and an object from a state a toa state f during a time interval from a time at which the object isgripped to a time at which the object starts to slip in a modelillustrated in FIG. 2.

FIG. 3B is a characteristic diagram illustrating a state where apressure-center position changes in each of regions of a first flexiblelayer and a second flexible layer in the states a to f illustrated inFIG. 3A.

FIG. 4 is a characteristic diagram illustrating, for comparison withFIG. 3B, a case where a friction coefficient of a first flexible layerand that of a second flexible layer are equalized to each other.

FIG. 5A is a diagram illustrating a dividing direction of the flexiblelayer.

FIG. 5B is a diagram illustrating a dividing direction of the flexiblelayer.

FIG. 5C is a diagram illustrating a dividing direction of the flexiblelayer.

FIG. 6 is a diagram illustrating a configuration example of a controlsystem of a robot according to one embodiment of the present disclosure.

FIG. 7 is a diagram illustrating a configuration of a gripping-forcecalculating unit according to a modification 1.

FIG. 8A is a characteristic diagram illustrating an example of pressuredistribution when the flexible layer is in contact with an object.

FIG. 8B is a characteristic diagram illustrating an example of pressuredistribution when the flexible layer is in contact with the object.

FIG. 8C is a characteristic diagram illustrating an example of pressuredistribution when the flexible layer is in contact with the object.

FIG. 9 is a diagram illustrating a configuration of a gripping-forcecalculating unit according to a modification 2.

FIG. 10 is a diagram illustrating a specific control of the hand.

FIG. 11 is a diagram illustrating a division example of a flexiblelayer.

FIG. 12 is a plan view illustrating a division example that does notdepend on a position in contact with an object.

FIG. 13 is a diagram illustrating an example in which distributionpressure sensors are displaced from each other and are arranged into alayer in order to artificially reduce a pitch width between nodes of thetwo distribution pressure sensors.

FIG. 14 is a diagram illustrating an example in which flexible layersare arranged on and under a distribution pressure sensor.

FIG. 15A is a diagram illustrating detection sensitivity by adistribution pressure sensor in accordance with difference in thicknessof a flexible layer.

FIG. 15B is a characteristic diagram illustrating states of examples (a)to (c) and a modification 4 that are illustrated in FIG. 15A, in which apressure-center position changes similarly to the case of FIG. 3B.

FIG. 16A is a diagram illustrating a reason that a moving direction of apressure-center position of the modification 4 is reverse to those ofthe examples (a) to (c).

FIG. 16B is a diagram illustrating a reason that a moving direction of apressure-center position of the modification 4 is reverse to those ofthe examples (a) to (c).

FIG. 17 is a diagram illustrating an example in which a surface area ofthe flexible layer is changed.

FIG. 18 is a diagram illustrating an example in which the hardness of alower-part flexible layer of the distribution pressure sensor is changedin order to change frictional force of an upper-part flexible layer ofthe distribution pressure sensor.

FIG. 19 is a diagram illustrating a configuration example using a linearflexible layer according to a modification 6.

FIG. 20 is a diagram illustrating a configuration of a gripping-forcecalculating unit using the linear flexible layer illustrated in FIG. 19.

FIG. 21 is a diagram illustrating an example in which flexible layersare arranged in multiple directions in the configuration using thelinear flexible layer illustrated in FIG. 19.

DESCRIPTION OF EMBODIMENTS

The following describes preferable embodiments of the present disclosurein detail with reference to the attached drawings. In the presentspecification and the drawings, overlap of descriptions will be avoidedby providing the same reference symbols for constituent elements havingsubstantially the same functional configuration.

Descriptions will be constituted in the following order.

1. Outline of Present Disclosure

2. Configuration of Hand

3. Slip of Object with respect to Flexible Layer

-   -   3.1. “Whole slip” and “Partial Slip”    -   3.2. Change in Contact State between Flexible Layer and Object    -   3.3. Determination of Slip based on Pressure-Center Position    -   3.4. Parameter that makes Occurrence Timing of Whole Slip        different for each Flexible Layer    -   3.5. Dividing Direction of Flexible Layer

4. Configuration Example of Control System of Robot

5. Modifications of Present Embodiment

-   -   5.1. Modification 1 (Example for Adjusting Gripping-Force        Controlling Gain in accordance with Rigidity of Object)    -   5.2. Modification 2 (Example for Controlling Position and        Posture of Finger in order to Increase Difference in Occurrence        Timing of Whole Slip)    -   5.3. Modification 3 (Variations of Arrangement of Flexible Layer        and Distribution Pressure Sensor)    -   5.4. Modification 4 (Example in which Flexible Layers are        Arranged to interpose Distribution Pressure Sensor therebetween)    -   5.5. Modification 5 (Method for Changing Friction Coefficient of        Flexible Layer)    -   5.6. Modification 6 (Example using Linear Flexible Layer)

1. Outline of Present Disclosure

For example, when a robot grips an object with a hand thereof, it isdesirable that the object is gripped with a moderate force having anextent to which the object does not slip off from the hand. Thus, theobject is able to be reliably gripped without breaking the object due toa gripping force. Particularly, when an object having the flexibility isgripped, breakage and deformation of the object is able to be reduced.The present disclosure relates to a technology that detects, in grippingan object, a state of “partial slip” before occurrence of a state of“whole slip” in which the object starts to slip, so as to grip theobject with an appropriate gripping force.

2. Configuration of Hand

FIG. 1 is a diagram illustrating a configuration of a hand 500 of arobot according to one embodiment of the present disclosure. The hand500 is arranged at a leading end of an arm 506 of a robot. Asillustrated in FIG. 1, the hand 500 includes a body 501, a link 512 anda link 514 constituting a first finger 502, and a link 516 and a link518 constituting a second finger 504. Joints 520, 522, 524, and 526 areprovided with respective actuators. The link 512 is turned with respectto the link 514 by driving force of an actuator of the joint 520, andthe link 514 is turned with respect to the body 501 by driving force ofan actuator of the joint 522. Similarly, the link 516 is turned withrespect to the link 518 by driving force of an actuator of the joint524, and the link 518 is turned with respect to the body 501 by drivingforce of an actuator of the joint 526.

The arm 506 as one example includes multiple joints, and a plurality oflinks is turnably connected by the joints. Driving force of an actuatorprovided to each of the joints causes corresponding links to turn withrespect to each other. Thus, the multiple-joint arm 506 is configured tohave a predetermined degree of freedom, and further to be able to movethe hand 500 to a desired position.

In FIG. 1, there is illustrated a state where the first finger 502 andthe second finger 504 grip an object (target gripped object) 600.Distribution pressure sensors 530 and 532 are arranged inside (on object600 side) of the link 512 of the first finger 502. A first flexiblelayer 540 is arranged inside of the distribution pressure sensor 530,and a second flexible layer 542 is arranged further inside of thedistribution pressure sensor 532. Similarly, distribution pressuresensors 530 and 532 are arranged inside (on object 600 side) of the link516 of the second finger 504. The first flexible layer 540 is arrangedinside of the distribution pressure sensor 530, and the second flexiblelayer 542 is arranged inside of the distribution pressure sensor 532.The first flexible layer 540 and the second flexible layer 542 are madeof an elastic material having one or both of the viscosity and theelasticity, are further made of a material that is easily deformed by aload applied from the outside, and made of material such as urethane geland silicone gel. The first flexible layer 540 is made of a materialwhose friction coefficient is smaller than that of the second flexiblelayer 542. A slip detecting device according to the present embodimentis constituted of the first and the second flexible layers 540 and 542and the distribution pressure sensors 530 and 532. The first and thesecond flexible layers 540 and 542 and the distribution pressure sensors530 and 532 may be directly attached to the arm 506. The first and thesecond flexible layers 540 and 542 and the distribution pressure sensors530 and 532 may be attached to a leg of a robot so as to detect a slipstate between the leg and the ground (floor). As described above, thefirst and the second flexible layers 540 and 542 and the distributionpressure sensors 530 and 532 may be attached to a working part withwhich a robot works on an object.

FIG. 2 is a diagram illustrating a state in which the first and thesecond flexible layers 540 and 542 of the first finger 502 are incontact with the object 600. Note that the object 600 illustrated inFIG. 1 is spherical-shaped, on the other hand, the object 600exemplified in FIG. 2 is rectangular parallelepiped-shaped. A directionof the x-axis illustrated in FIG. 2 is a direction (or direction inwhich object 600 is going to slip) in which the object 600 relativelyslips with respect to the first and the second flexible layers 540 and542. As illustrated in FIG. 2, the two flexible layers 540 and 542 arearranged such that the second flexible layer 542 and the first flexiblelayer 540 are arranged in this order in a slipping direction of theobject 600, and thus according to this arrangement, difference in anoccurrence timing of a whole slip between the first flexible layer 540and the second flexible layer 542 is able to be enlarged. In the exampleillustrated in FIG. 1, the x-axis direction corresponds to the gravitydirection.

As illustrated in FIG. 2, a force Ft is applied to the object 600 in thex-axis direction. When the x-axis direction is the gravity direction,the force Ft corresponds to the gravity. A force Fn is applied to theobject 600 in the y-axis direction that is perpendicular to the x-axisdirection. The force Fn corresponds to a reaction force when the object600 is gripped by the first finger 502 and the second finger 504.

3. Slip of Object with Respect to Flexible Layer

3.1. “Whole Slip” and “Partial Slip”

As illustrated in FIG. 2, the force Ft is applied to the object 600 inthe x-axis direction. In a case where the gravity direction is thex-axis direction, when a gripping force is weak with which the firstfinger 502 and the second finger 504 are gripping the object 600, theobject 600 slips off in the gravity direction. Transition from a statewhere the object 600 is stopped to a state where the object 600 startsto slip is able to be explained by phenomenon of “whole slip” and“partial slip”.

The “whole slip” is a state in which a relative position between theobject 600 and the flexible layer deviates, and thus an object isslipping off. The “partial slip” is a phenomenon that occurs before the“whole slip” and in which a part of a contact surface between the object600 and the flexible layers 540 and 542 is slipping. In the presentembodiment, “partial slip” is detected in which the object 600 isgripped with the minimum force having an extent to which the object 600does not slip off when the object 600 is gripped.

3.2. Change in Contact State Between Flexible Layer and Object

FIG. 3A is a diagram schematically illustrating chronological change ina contact state between the flexible layers 540 and 542 and the object600 from a state a to a state f during a time interval from a time atwhich the object 600 is gripped to a time at which the object 600 startsto slip in a model illustrated in FIG. 2. In FIG. 3A, an upper surfaceof each of the flexible layers 540 and 542 is divided into a pluralityof rectangular regions, and a contact state with the object 600 isclassified into two of “sticking” and “slipping” by using two types ofdots provided to the rectangular regions. In a rectangular region of“sticking”, a slip does not occur between the object 600 and theflexible layers 540 and 542, and thus the object 600 and the flexiblelayers 540 and 542 stick to each other. On the other hand, in arectangular region of “slipping”, a slip has occurred between the object600 and the flexible layers 540 and 542. The states of the rectangularregions may be obtained by analysis using simulation, for example.Hereinafter, on the basis of illustration of FIG. 3A, a state will beexplained in which “partial slip” and “whole slip” occur during a timeinterval from a time at which the object 600 is gripped to a time atwhich the object 600 starts to slip.

A flexible layer arranged on the distribution pressure sensors 530 and532 is divided into, for example, two parts of the first flexible layer540 and the second flexible layer 542, and by the division, the firstflexible layer 540 and the second flexible layer 542 are aligned in aslipping direction (x-axis direction) of the object 600. In the state aillustrated in FIG. 3A, all of the rectangular regions of upper surfacesof the first flexible layer 540 and the second flexible layer 542 are ina “sticking” state. Next, in the state b, rectangular regions in theupper surface of the first flexible layer 540 which are close to thesecond flexible layer 542 are changed into a “slipping” state. The otherregions are in a “sticking” state.

Next, in the state c illustrated in FIG. 3A, in the upper surface of thefirst flexible layer 540, rectangular regions in a “slipping” state haveenlarged. In the next state d, all of the rectangular regions in theupper surface of the first flexible layer 540 are changed into a“slipping” state, and a part of rectangular regions in the upper surfaceof the second flexible layer 542 is changed into a “slipping” state. Inthe next state e, in the upper surface of the second flexible layer 542,rectangular regions in a “slipping” state have enlarged. In the nextstate f, all of the rectangular regions in the upper surface of thesecond flexible layer 542 are changed into a “slipping” state.

When all of the rectangular regions in each of the first flexible layer540 and the second flexible layer 542 are changed into a “slipping”state, a corresponding “whole slip” state appears. The first flexiblelayer 540 is turned into a “whole slip” state in the state d, andremains the “whole slip” state in the states e and f after the state d.On the other hand, the second flexible layer 542 is turned, later thanthe first flexible layer 540, into a “whole slip” state in the state f.

As described above, in each of the first flexible layer 540 and thesecond flexible layer 542, “slipping” regions are enlarged over time toturn into a “whole slip” state, and it is found that a timing at whichthe first flexible layer 540 having a low friction coefficient is turnedinto a “whole slip” state is earlier. In other words, when frictioncoefficients of the two flexible layers 540 and 542 are different fromeach other, it is possible to generate difference in an occurrencetiming of a whole slip.

In the state f where a whole slip simultaneously occurs in two regionsof the first flexible layer 540 and the second flexible layer 542, awhole slip has occurred in all of the regions including the firstflexible layer 540 and the second flexible layer 542. In the state, theobject 600 relatively moves with respect to both of the first flexiblelayer 540 and the second flexible layer 542, and in FIG. 2, the object600 is slipping in the x-axis direction.

In the present embodiment, the states d and e in each of which a wholeslip occurs in a region of one of the first flexible layer 540 and thesecond flexible layer 542, and a whole slip does not occur in a regionof the other are defined as a state where “partial slip” has occurred inall of the regions including the first flexible layer 540 and the secondflexible layer 542. In the states d and e in which “partial slip” hasoccurred, the object 600 does not relatively move with respect to thefirst flexible layer 540 and the second flexible layer 542. In FIG. 3A,in order to indicate that the states d and e are in a “partial slip”state, the states d and e are surrounded by bold lines.

When focusing on a region of one of the first flexible layer 540 and thesecond flexible layer 542, it may be interpreted that in a region of thefirst flexible layer 540 under the states b and c, or in a region of thesecond flexible layer 542 under the states d and e, a partial slip hasoccurred. However, in the present embodiment, when all of the regionsincluding the first flexible layer 540 and the second flexible layer 542are focused on, the states d and e in which a whole slip has occurred ina region of one of the flexible layers 540 and 542 and a whole slip hasnot occurred in a region of the other are defined as a state where“partial slip” has occurred in all of the regions.

Each of the states a to c in which a whole slip has not occurred in thefirst flexible layer 540 or the second flexible layer 542 is a state inwhich all of the regions including the first flexible layer 540 and thesecond flexible layer 542 are sticking to the object 600.

Thus, each of the states d and e in which “partial slip” has occurred isa state just before the object 600 starts to slip, and the object 600does not relatively move with respect to the first flexible layer 540and the second flexible layer 542. Thus, when a “partial slip” state isdetected and an object is gripped with a gripping force having an extentto which a partial slip occurs, deformation and breakage of the object600 is able to be reduced, and the object 600 is able to be gripped withan appropriate force with which the object 600 does not slip.

3.3. Determination of Slip Based on Pressure-Center Position

In the present embodiment, that “partial slip” or “whole slip” hasoccurred in all of the regions including the first flexible layer 540and the second flexible layer 542 is determined on the basis ofpressure-center positions obtained from the distribution pressuresensors 530 and 532.

FIG. 3B is a characteristic diagram illustrating a state where apressure-center position changes in each of regions of the firstflexible layer 540 and the second flexible layer 542 in the states a tof illustrated in FIG. 3A. A pressure-center position X_(cop) is obtainedfrom the following formula (1). Each of the distribution pressuresensors 530 and 532 includes a plurality of nodes for detecting thepressure, which is arranged in a matrix. In the formula (1), N is thenumber of sensor nodes of each of the distribution pressure sensors 530and 532, x_(i) is a coordinate of an i-th node, and p(x_(i)) is apressure detected by the i-th node. The pressure-center position X_(cop)is a value obtained by dividing, by a total of pressure values, a totalof values that are obtained by multiplying the pressure values bycoordinates, and is a value indicating the pressure center of each ofthe distribution pressure sensors 530 and 532.

$\begin{matrix}{X_{cop} = \frac{\sum_{0}^{N - 1}\left\{ {{p\left( x_{i} \right)} \cdot x_{i}} \right\}}{\sum_{0}^{N - 1}{p\left( x_{i} \right)}}} & (1)\end{matrix}$

In FIG. 3B, from the left, change in a pressure-center position of thesecond flexible layer 542, change in a pressure-center position of thefirst flexible layer 540, and change in the pressure-center positions ofthe first and the second flexible layers 540 and 542 are indicated inthis order. In the three characteristic diagrams, a lateral axis is anumber indicating the number of time steps, and a vertical axisindicates a pressure-center position. A pressure-center position of thevertical axis corresponds to a position in the x-axis directionillustrated in FIG. 2. In the characteristic of the first flexible layer540, the origin of the vertical axis corresponds to the originillustrated in FIG. 2, and in the characteristic of the second flexiblelayer 542, the origin of the vertical axis corresponds to a coordinateof −L illustrated in FIG. 2. Assume that a length in the x-axisdirection of the first flexible layer 540 and that of the secondflexible layer 542 are the same (=L).

In FIG. 3B, a to f provided to the characteristic of a pressure-centerposition respectively correspond to the states a to f illustrated inFIG. 3A.

As illustrated in FIG. 3B, as time passes, each of pressure-centerpositions of the first and the second flexible layers 540 and 542 movesin the x-axis direction illustrated in FIG. 2. In this case, apressure-center position of the first flexible layer 540 having a lowerfriction coefficient moves faster than that of the second flexible layer542. In the first flexible layer 540, at a time point when the number oftime steps exceeds 15, movement of a pressure-center position stops tobe turned into a steady state in which the pressure-center position is aconstant value. On the other hand, in the second flexible layer 542, ata time point when the number of time steps exceeds 25, movement of apressure-center position stops to be turned into a steady state in whichthe pressure-center position is a constant value.

As illustrated in FIG. 3B, a state where movement of a pressure-centerposition is stopped in each of the first flexible layer 540 and thesecond flexible layer 542 corresponds to a “whole slip” state. On theother hand, a state where movement of a pressure-center position is notstopped in each of the first flexible layer 540 and the second flexiblelayer 542 is a state where the corresponding pressure-center position ismoving due to shear deformation and a partial slip of the first flexiblelayer 540 or the second flexible layer 542. In the state where movementof a pressure-center position is not stopped, a relative movement doesnot occur between the object 600 and the first flexible layer 540 andthe second flexible layer 542. On the other hand, in a state wheremovement of a pressure-center position is not stopped, in some cases, anabsolute position of the object 600 is changed due to shear deformationof the first flexible layer 540 or the second flexible layer 542. Asdescribed above, when friction coefficients of the two flexible layers540 and 542 are different from each other, it is possible to generatedifference in an occurrence timing of a whole slip, as obvious from FIG.3B, an occurrence timing at which a whole slip of the second flexiblelayer 542 is later than that of the first flexible layer 540.

The characteristic diagram illustrated on the right side of FIG. 3B is acharacteristic diagram obtained by overlapping the characteristicdiagram illustrated on the left side of FIG. 3B and the characteristicdiagram illustrated in the center of FIG. 3B. In the present embodiment,on the basis of change in a pressure-center position, a state where awhole slip has occurred in the first flexible layer 540 in which a wholeslip occurs earlier and a whole slip has not occurred in the secondflexible layer 542 is determined to be a state where “partial slip” hasoccurred in a whole region including the first flexible layer 540 andthe second flexible layer 542. Furthermore, on the basis of change in apressure-center position, a state where a whole slip has occurred inboth of the first flexible layer 540 and the second flexible layer 542is determined to be a state where “whole slip” has occurred in a wholeregion including the first flexible layer 540 and the second flexiblelayer 542. Furthermore, on the basis of change in a pressure-centerposition, a state where a whole slip has not occurred in both of thefirst flexible layer 540 and the second flexible layer 542 is determinedto be a sticking state.

As described above, when a pressure-center position is calculated in aregion of each of the first flexible layer 540 and the second flexiblelayer 542, a whole slip in the corresponding region is able to bedetected. In the above-mentioned example, the number of regions is two,and thus when a whole slip simultaneously occurs in the two regions, thestate is determined that a whole slip has occurred in a whole regionincluding the first flexible layer 540 and the second flexible layer 542(state f). When a whole slip has occurred in one of the regions, thestate is determined that a partial slip has occurred in a whole region(states d and e). When a whole slip has not occurred in any of theregions, the state is determined that a whole region is in a “stickingstate” (states a, b, and c).

Assume that a rate of a non-detection region of “whole slip” withrespect to a whole region (contact region of target object 600)including the first flexible layer 540 and the second flexible layer 542is a sticking rate. In FIG. 3B, in the state f, with respect to a wholeregion including the first flexible layer 540 and the second flexiblelayer 542, both of a region of the first flexible layer 540 and a regionof the second flexible layer 542 are in a state of a whole slip, andthus a sticking rate is 0%.

In the states d and e, with respect to a whole region including thefirst flexible layer 540 and the second flexible layer 542, a region ofthe first flexible layer 540 is in a state of a whole slip, and thus asticking rate is 50%. In the states a, b, and c, with respect to a wholeregion including the first flexible layer 540 and the second flexiblelayer 542, none of a region of the first flexible layer 540 and a regionof the second flexible layer 542 are in a state of a whole slip, andthus a sticking rate is 100%.

In the present embodiment, a gripping force by the hand 500 iscontrolled in accordance with a sticking rate. As a sticking rate islarger, a gripping force by the hand 500 is more reduced, and as asticking rate is smaller, a gripping force by the hand 500 is moreincreased. Thus, the object 600 is able to be gripped with the bareminimum force, so that it is possible to prevent breakage anddeformation of the object 600.

As the number of division in a region of the flexible layer is larger,the resolution of a sticking rate is larger, and further the accuracy ofgripping force control is higher. Moreover, as the number of division ina region of the flexible layer is larger, with respect to a smallerobject and an object having concavity and convexity, a sticking rate isable to be detected. For example, in a case where the number of divisionin the flexible layer is three, when a sticking rate is obtained by amethod similar to the above-mentioned one, a sticking rate is able to becalculated with four steps of 0%, 33%, 66%, and 100%.

For example, in a case where the number of division in the flexiblelayer is three and a friction coefficient of each of the dividedflexible layers are different from each other, when a whole slip hasoccurred in all of the flexible layers, a sticking rate is 0%. When awhole slip has occurred in a region of a flexible layer whose frictioncoefficient is the smallest and a region of a flexible layer whosefriction coefficient is the second smallest, and a whole slip has notoccurred in a region of a flexible layer whose friction coefficient isthe largest, a sticking rate is 33%. When a whole slip has occurred in aregion of a flexible layer whose friction coefficient is the smallest,and a whole slip has not occurred in a region of a flexible layer whosefriction coefficient is the second smallest and a region of a flexiblelayer whose friction coefficient is the largest, a sticking rate is 66%.Furthermore, when a whole slip has occurred in all of the regions of theflexible layers, a sticking rate is 0%. From a similar viewpoint, as thenumber of division in a region of a flexible layer is more increased, astate of a partial slip is able to be detected with a higher accuracy.

FIG. 4 is a characteristic diagram illustrating, for comparison withFIG. 3B, a case where a friction coefficient of the first flexible layer540 and that of the second flexible layer 542 are equalized to eachother. Conditions other than a friction coefficient and an indicatingmethod of characteristic diagrams are similar to those illustrated inFIG. 3B. As illustrated in FIG. 4, when a friction coefficient of thefirst flexible layer 540 and that of the second flexible layer 542 arethe same to each other, there presents no difference in an occurrencetiming of a whole slip between a region of the first flexible layer 540and a region of the second flexible layer 542, and thus it is difficultto detect a partial slip in a whole region including the first flexiblelayer 540 and the second flexible layer 542. Thus, a state according tothe present embodiment illustrated in FIG. 3B where a sticking rate is50%, in other words, a state where “partial slip” has occurred in awhole region including the first flexible layer 540 and the secondflexible layer 542 is not able to be detected. According to the presentembodiment, a state where “partial slip” has occurred is able to bedetected in a whole region including the first flexible layer 540 andthe second flexible layer 542, and thus a gripping force is able to becontrolled with high accuracy on the basis of a sticking ratecorresponding to a state of a partial slip.

Thus, when friction coefficients of the first flexible layer 540 and thesecond flexible layer 542 are different from each other, it is possibleto generate difference in an occurrence timing of a whole slip betweenthe first flexible layer 540 and the second flexible layer 542, so thatit is possible to detect a partial slip in a whole region including thefirst and the second flexible layers 540 and 542. As difference in anoccurrence timing of a whole slip between the first flexible layer 540and the second flexible layer 542 is larger, a time interval duringwhich a partial slip occurs in a whole region including the first andthe second flexible layers 540 and 542 is longer, so that it is possibleto easily control a gripping force.

3.4. Parameter that Makes Occurrence Timing of Whole Slip Different forEach Flexible Layer

In the above explanation, friction coefficients are made different fromeach other between the first flexible layer 540 and the second flexiblelayer 542 so as to make an occurrence timing of a whole slip differentbetween the first flexible layer 540 and the second flexible layer 542.On the other hand, parameters other than the friction coefficients maybe made different from each other between the first flexible layer 540and the second flexible layer 542, so as to make an occurrence timing ofa whole slip different between the first flexible layer 540 and thesecond flexible layer 542. As parameters other than a frictioncoefficient, the Young's modulus, the Poisson ratio, thickness, acurvature radius, and the like may be exemplified.

In a case of a friction coefficient, as a friction coefficient issmaller, an occurrence timing of a whole slip is earlier. In a case ofthe Young's modulus, as the Young's modulus is larger, an occurrencetiming of a whole slip is earlier. In a case of the Poisson ratio, asthe Poisson ratio is smaller, an occurrence timing of a whole slip isearlier. In a case of the thickness, as the thickness is smaller, anoccurrence timing of a whole slip is earlier. In a case of a curvatureradius, as a curvature radius is larger, an occurrence timing of a wholeslip is earlier.

In the above-mentioned parameters, when conditions both of whoseoccurrence timings of a whole slip are early, or conditions both ofwhose occurrence timings of a whole slip are late are combined with eachother, it is possible to further increase difference in an occurrencetiming of a whole slip. For example, when a first flexible layer whosefriction coefficient is small and thickness is small and a secondflexible layer whose friction coefficient is large and thickness islarge are provided, it is possible to further increase difference in anoccurrence timing of a whole slip between the first flexible layer andthe second flexible layer.

3.5. Dividing Direction of Flexible Layer

FIGS. 5A to 5C are diagrams illustrating dividing directions of theflexible layer. Similarly to FIGS. 1 and 2, in FIGS. 5A and 5B, examplesare illustrated in which the first flexible layer 540 and the secondflexible layer 542 are divided into two parts in a slipping direction.In FIG. 5C, an example is illustrated in which the first flexible layer540 and the second flexible layer 542 are divided into two parts in adirection perpendicular to the slipping direction.

When a vertical axis (z-axis illustrated in FIGS. 5A to 5C) of theobject 600 to be gripped is restricted with respect to a slippingdirection of the object 600, there presents no difference in anoccurrence timing of a complete slip between the first flexible layer540 and the second flexible layer 542. On the other hand, when thevertical axis is not restricted, an axial rotation is slightly generateddue to friction distribution, and thus difference in an occurrencetiming of a complete slip is larger when the first flexible layer 540and the second flexible layer 542 are vertically divided with respect toa slipping direction. In an actual environment, there presents nosituation in which an axis of an object is restricted, and thus a caseis more preferable in which the first flexible layer 540 and the secondflexible layer 542 are divided with respect to a slipping direction, asillustrated in FIGS. 5A and 5B. Moreover, a case illustrated in FIG. 5Ain which the second flexible layer 542 and the first flexible layer 540are arranged in this order with respect to a slipping direction of theobject 600 has a larger difference in an occurrence timing of a wholeslip than a case illustrated in FIG. 5B in which the first flexiblelayer 540 and the second flexible layer 542 are arranged in this orderwith respect to a slipping direction of the object 600. In other words,when the second flexible layer 542 having a larger friction coefficientis arranged on an upper flow side of a slipping direction, difference inan occurrence timing of a whole slip between the first flexible layer540 and the second flexible layer 542 is able to be larger. In a case ofarrangement illustrated in FIG. 5B, a slipping force of the firstflexible layer 540 positioned on an upper flow side of a slippingdirection is stopped by the second flexible layer 542 positioned on alower flow side, and thus an occurrence timing of a whole slip in thefirst flexible layer 540 becomes comparatively late. Thus, in a case ofarrangement illustrated in FIG. 5B, difference in an occurrence timingof a whole slip between the first flexible layer 540 and the secondflexible layer 542 becomes comparatively small. On the other hand, in acase of arrangement illustrated in FIG. 5A, a slipping force of thesecond flexible layer 542 positioned on an upper flow side of a slippingdirection is not stopped by the first flexible layer 540 positioned on alower flow side, and thus a whole slip occurs at a comparatively earlytiming in the first flexible layer 540 positioned on a lower flow side.Thus, in a case of arrangement illustrated in FIG. 5A, difference in anoccurrence timing of a whole slip is able to be larger.

The plurality of flexible layers may be arranged to be adjacent to eachother. For example, as illustrated in FIG. 10 to be mentioned later, thefirst flexible layer 540 and the second flexible layer 542 may beseparately and respectively arranged in different fingers of the hand500.

4. Configuration Example of Control System of Robot

FIG. 6 is a diagram illustrating a configuration example of a controlsystem (controller) 1000 of a robot according to one embodiment of thepresent disclosure. As illustrated in FIG. 6, the control system 1000 isconfigured to include a recognizing/planning unit 100, a gripping-forcecalculating unit 200, and a control unit 300. The recognizing/planningunit 100 includes a recognition unit 102, a command unit 104, agripping-position deciding unit 106, and an operation planning unit 108.The gripping-force calculating unit 200 includes a pressure acquiringunit 202, a touch detecting unit 204, a pressure-center-positioncalculating unit 206, a pressure-center movement-amount calculating unit208, a whole-slip detecting unit 210, a sticking-rate calculating unit212, and a gripping-force controlling unit 214. The control unit 300includes an overall control unit 302 and a hand controlling unit 304.

The recognizing/planning unit 100 recognizes the object 600 to begripped by a robot, and creates a plan for gripping the object 600. Therecognition unit 102 is constituted of a camera, a Time of Flight (ToF)sensor, etc. so as to recognize a three-dimensional shape of the object600. A command from a user is input to the command unit 104. Thegripping-position deciding unit 106 decides, by using recognition resultof a target object by the recognition unit 102, a position of a robotfor gripping the object 600 on the basis of a command of a user which isinput to the command unit 104. On the basis of a gripping positiondecided by the gripping-position deciding unit 106, the operationplanning unit 108 creates a plan of operation of the arm 506 andoperation of the hand 500 arranged at a leading end of the arm 506 ofthe robot.

The gripping-force calculating unit 200 calculates a gripping force ofthe hand 500 for gripping the object 600 so as to control the grippingforce. The pressure acquiring unit 202 acquires a pressure detected bythe distribution pressure sensors 530 and 532. The touch detecting unit204 detects, by using a distribution pressure value acquired by thepressure acquiring unit 202, contact between the first and the secondflexible layers 540 and 542 and the object 600. For example, when adistribution pressure value is equal to or more than a predeterminedvalue, the touch detecting unit 204 detects contact between the firstand the second flexible layers 540 and 542 and the object 600. Thepressure-center-position calculating unit 206 calculates, by using adistribution pressure value acquired by the pressure acquiring unit 202,a pressure-center position X_(cop) in accordance with theabove-mentioned formula (1) in a region of each of the first and thesecond flexible layers 540 and 542.

The pressure-center movement-amount calculating unit 208 calculates, byusing a pressure-center position calculated by thepressure-center-position calculating unit 206, a movement amount of apressure-center position in a region of each of the first and the secondflexible layers 540 and 542. The pressure-center movement-amountcalculating unit 208 calculates a movement amount ΔX_(cop) of apressure-center position by the following formula (2). The right side ofthe formula (2) indicates a difference between the pressure-centerposition X_(cop) at a time point t+1 and the pressure-center positionX_(cop) at a time point t.

ΔX _(cop) =X _(cop) _(τ+1) −X _(cop) _(τ)   (2)

The whole-slip detecting unit 210 detects, by using a movement amount ofa pressure-center position calculated by the pressure-centermovement-amount calculating unit 208, whether or not there presents achange in movement of a pressure-center position during apreliminary-set time window. The time window is a predetermined timeinterval that has been preliminary set. When there presents no movementof a pressure-center position during the predetermined time interval,the whole-slip detecting unit 210 detects that the pressure-centerposition is not changed and a whole slip has occurred. The whole-slipdetecting unit 210 monitors change in a pressure-center position foreach of the regions of the two distribution pressure sensors 530 and532, so as to detect occurrence of a whole slip in each of the regions.

The sticking-rate calculating unit 212 calculates a rate of anon-detection region of a whole slip with respect to a whole regionincluding the first flexible layer 540 and the second flexible layer542, and employs the calculated rate as a sticking rate. As describedabove, when the flexible layer is divided into two parts, the stickingrate is calculated as three-type values of 0%, 50%, and 100%.

The gripping-force controlling unit 214 decides a gripping force suchthat a sticking rate is a constant value. The gripping-force controllingunit 214 controls, by feedback control, a gripping force such that asticking rate calculated by the sticking-rate calculating unit 212 is apredetermined value. As one example, the gripping-force controlling unit214 controls a gripping force such that a sticking rate is 50%.

The control unit 300 controls operation of a robot. On the basis of anoperation plan created by the operation planning unit 108, the overallcontrol unit 302 controls the arm 506 of the robot. On the basis ofcontrol of the gripping-force controlling unit 214, the hand controllingunit 304 controls the hand 500. Note that the gripping-force controllingunit 214 and the hand controlling unit 304 may be integrated with eachother.

Each of the configuration elements of the recognizing/planning unit 100,the gripping-force calculating unit 200, and the control unit 300 of thecontrol system 1000 illustrated in FIG. 6 may be constituted of acircuit (hardware) or a center calculation processing device such as aCentral Processing Unit (CPU) and a program (software) that causes theCPU to function.

The program may be stored in a memory provided to the control system1000, or a recording medium, such as a memory, which is connected to thecontrol system 1000 from the outside thereof. The same may be applied toFIGS. 7, 9, and 20 to be mentioned later.

5. Modifications of Present Embodiment

Hereinafter, a few modifications of the present embodiment will beexplained.

5.1. Modification 1 (Example for Adjusting Gripping-Force ControllingGain in Accordance with Rigidity of Object)

In a modification 1, physical information (rigidity) on the object 600is calculated from a position of the hand 500 at a moment when theobject 600 is in contact with a flexible layer and then the flexiblelayer is pressed against the object 600, or information on a contactarea and a contact force between the flexible layer and the object 600.A gripping-force controlling gain is adjusted on the basis of thephysical information on the object 600. The gripping-force controllinggain is an increase rate when a gripping force is increased such that asticking rate is a constant value.

FIG. 7 is a diagram illustrating a configuration of the gripping-forcecalculating unit 200 according to the modification 1. As illustrated inFIG. 7, the gripping-force calculating unit 200 according to themodification 1 includes, in addition to the configuration illustrated inFIG. 6, a contact-force calculating unit 216, a contact-node-numberacquiring unit (contact-radius calculating unit) 218, and aphysical-information calculating unit 220.

The contact-force calculating unit 216 calculates a contact force whenthe object 600 is in contact with the first and the second flexiblelayers 540 and 542. The contact force is obtained by multiplying thenumber of contact nodes of all of the nodes of the distribution pressuresensors 530 and 532 by a force (pressure) applied to each of the contactnodes. The contact node is a node of the distribution pressure sensors530 and 532 which is in contact with the object 600 via the firstflexible layer 540 or the second flexible layer 542. In other words, thecontact node is a node from which a detection value (detection value isnot zero) of the pressure is obtained.

On the basis of contact between the first and the second flexible layers540 and 542 and the object 600 which is detected by the touch detectingunit 204, the contact-node-number acquiring unit 218 acquires a contactnode number. The contact node number corresponds to a contact area. Frominformation on a contact area acquired from the contact-node-numberacquiring unit 218 and information on a contact force acquired from thecontact-force calculating unit 216, the physical-information calculatingunit 220 calculates rigidity as physical information on the object 600.

From a contact radius a when the object 600 is in contact with aflexible layer, the rigidity is able to be calculated as physicalinformation on the object 600. In this case, a contact-radiuscalculating unit is caused to function instead of thecontact-node-number acquiring unit 218. From the Hertz contact theory,the contact radius a between a robot finger (first finger 502 or secondfinger 504) and an object is able to be indicated by the followingformula (3).

$\begin{matrix}{a = \left( \frac{3F_{n}r}{4E^{*}} \right)^{\frac{1}{2}}} & (3)\end{matrix}$

Note that r is a radius of a robot finger, and E* is an effectiveelastic modulus. As indicated in the following formula (4), theeffective elastic modulus E* is obtained by elastic moduli Ef and Eo andrespective Poisson ratios of and vo of the robot finger and the object.

$\begin{matrix}{E^{*} = \left( {\frac{1 - v_{f}^{2}}{E_{f}} + \frac{1 - v_{o}^{3}}{E_{o}}} \right)^{- 1}} & (4)\end{matrix}$

The Poisson ratio is a value that is not more than approximately 0.5 andis commonly a smaller value, and thus the Poisson ratio is able to beneglected as indicated in a formula (5) by assuming that a value of thesquare of the Poisson ratio does not largely affect E.

$\begin{matrix}{\left. E^{*} \right.\sim\left( {\frac{1}{E_{f}} + \frac{1}{E_{o}}} \right)^{- 1}} & (4)\end{matrix}$

A radius r of a robot finger and the Young's modulus Ef of the robotfinger are already known, and thus on the basis of the contact radius acalculated by the contact-radius calculating unit 218 and information ona contact force Fn, physical information (Young's modulus Eo) on theobject 600 is able to be calculated by the formula (3).

The rigidity as physical information on the object 600 is transmitted tothe gripping-force controlling unit 214. The gripping-force controllingunit 214 adjusts a gripping-force controlling gain on the basis of thephysical information. As described above, a gripping-force controllinggain is an increase rate when a gripping force is increased such that asticking rate is a predetermined constant value. When the rigidity ofthe object 600 is high, probability that deformation or breakage occursin the object 600 is comparatively low, and thus the gripping-forcecontrolling unit 214 sets an increase rate of a gripping force to behigh when controlling a sticking rate such that the sticking rate is atarget value. On the other hand, when the rigidity of the object 600 islow, probability that deformation or breakage occurs in the object 600is comparatively high, and thus the gripping-force controlling unit 214sets an increase rate of a gripping force to be low when controlling asticking rate such that the sticking rate is a target value.

According to the modification 1, the above-mentioned state of a partialslip is detected, a gripping force is able to be controlled with thebare minimum force having an extent to which the object 600 does notslip, and further an increase rate of a gripping force is able to becontrolled in accordance with the hardness of the object 600. Thus, itis possible to reliably reduce deformation and breakage of the object600 in gripping.

When obtaining a rigidity of the object 600, the rigidity may beobtained by relation between a position (pressed amount) of the hand 500and a contact force obtained from the distribution pressure sensors 530and 532 when a flexible layer is pressed against the object 600.

5.2. Modification 2 (Example for Controlling Position and Posture ofFinger in Order to Increase Difference in Occurrence Timing of WholeSlip)

In a modification 2, a position and a posture of a finger are controlledin order to increase difference in an occurrence timing of a whole slipbetween the first flexible layer 540 and the second flexible layer 542.Herein, as pressure distribution is steeper when the flexible layers 540and 542 are in contact with the object 600, an occurrence timing of awhole slip is later. FIGS. 8A to 8C are characteristic diagramsillustrating examples of pressure distribution when the flexible layers540 and 542 are in contact with the object 600. FIG. 8C, FIG. 8B, andFIG. 8A are aligned in the decreasing order of steepness of a pressuredistribution. That a pressure distribution is steep means that apressure gradient is large in an end part of a region (region A1illustrated in FIGS. 8A to 8C) in which the flexible layers 540 and 542and the object 600 are in contact with each other.

In FIGS. 8A to 8C, a region in which the pressure is high is a region inwhich the flexible layers 540 and 542 are in contact with the object600. In an end part of a region in which the flexible layers 540 and 542and the object 600 are in contact with each other, a gradient isgenerated in the pressure. As the pressure gradient is larger, anoccurrence timing of a whole slip is later.

For example, in a region in which the flexible layers 540 and 542 andthe object 600 are in contact with each other, a shape of the object 600has a convex surface, and as a curvature radius of the convex surface issmaller, a pressure gradient is steeper and an occurrence timing of awhole slip is later.

In the modification 2, the hand 500 is controlled such that the firstflexible layer 540 and the second flexible layer 542 are arranged inrespective positions having different pressure gradients for each of thefirst flexible layer 540 and the second flexible layer 542.

FIG. 9 is a diagram illustrating a configuration of the gripping-forcecalculating unit 200 according to the modification 2. As illustrated inFIG. 9, the gripping-force calculating unit 200 according to themodification 2 includes a pressure-gradient calculating unit 222 and anactuator controlling unit 224 in addition to the configurationillustrated in FIG. 6.

When contact between the first and the second flexible layers 540 and542 and the object 600 is detected by the touch detecting unit 204, thepressure-gradient calculating unit 222 acquires the features illustratedin FIGS. 8A to 8C on the basis of pressures detected by the distributionpressure sensors 530 and 532. The pressure-gradient calculating unit 222calculates a pressure gradient of the region A1 illustrated in FIGS. 8Ato 8C. Note that pressures detected by the distribution pressure sensors530 and 532 are acquired by the pressure acquiring unit 202, and aretransmitted to the pressure-gradient calculating unit 222.

On the basis of a pressure gradient calculated by the pressure-gradientcalculating unit 222, the actuator controlling unit 224 controls anactuator that controls the hand 500 or the arm 506. The actuatorcontrolling unit 224 controls the actuator such that the object 600 isgripped at a position where difference in a pressure gradient is largerin a contact part between the first flexible layer 540 and the secondflexible layer 542 and the object 600.

FIG. 10 is a diagram illustrating a specific control of the hand 500. InFIG. 10, a state before a position and a posture of a finger arecontrolled in accordance with pressure gradient is illustrated in a leftpart, and a state after a position and a posture of a finger arecontrolled in accordance with pressure gradient is illustrated in aright part. In FIG. 10, the first flexible layer 540 and thedistribution pressure sensor 530 are provided to the first finger 502,and the second flexible layer 542 and the distribution pressure sensor532 are provided to the second finger 504. Thus, in FIG. 10, an exampleis illustrated in which the first flexible layer 540 and the secondflexible layer 542 are not divided in a slipping direction of the object600.

Before a position and a posture of a finger are controlled, a contactsurface of the object 600 is a curved surface for each of the firstflexible layer 540 and the second flexible layer 542. On the other hand,after a position and a posture of a finger are controlled, a contactsurface of the object 600 is a curved surface for the second flexiblelayer 542; however, a contact surface of the object 600 is a plane forthe first flexible layer 540.

As described above, a friction coefficient of the first flexible layer540 is smaller than a friction coefficient of the second flexible layer542, and thus an occurrence timing of a whole slip of the secondflexible layer 542 is later. Additionally, after a position and aposture of a finger is controlled, a contact surface of the object 600is a plane for the first flexible layer 540, and a contact surface ofthe object 600 is a curved surface for the second flexible layer 542.Thus, a pressure distribution in the second flexible layer 542 issteeper than a pressure distribution of the first flexible layer 540,and thus an occurrence timing of a whole slip in the second flexiblelayer 542 is further later. Thus, difference in an occurrence timing ofa whole slip is able to be larger between the first flexible layer 540and the second flexible layer 542.

In the above-mentioned example, the example is indicated in which aposition and a posture of a finger of the hand 500 is controlled inaccordance with pressure gradient; however, a position and a posture ofa finger of the hand 500 may be controlled on the basis ofthree-dimensional information on the object 600 which is obtained byobserving a shape of the object 600 by using the recognition unit 102.In this case, on the basis of the three-dimensional information, thefirst flexible layer 540 may be caused to be in contact with a parthaving a small pressure gradient and the second flexible layer 542 maybe caused to be in contact with a part having a large pressure gradient.

5.3. Modification 3 (Variations of Arrangement of Flexible Layer andDistribution Pressure Sensor)

As described above, it is more preferable that the first flexible layer540 and the second flexible layer 542 are divided in a slippingdirection of the object 600. In a modification 3, when a plurality ofslipping directions of the object 600 is supposed in accordance with aposture of the hand 500 and/or the arm 506, division is executed whichdoes not depend on a slipping direction.

FIG. 11 is a diagram illustrating a division example of a flexiblelayer. In the example illustrated in FIG. 11, the Young's modulus isdifferent for each of a plurality of flexible layers 544, 546, 548, and550. The flexible layers 544, 546, 548, and 550 are divided by circularboundaries, and the closer to the center, the smaller the Young'smodulus is. According to such a division method, it is possible tocorrespond to slips in multiple directions which are indicated in FIG.11 by using a plurality of arrows, and for each of the slippingdirections, a flexible layer is divided in a corresponding slippingdirection.

As described above, in a parameter that makes an occurrence timing of awhole slip different for each flexible layer, when conditions whoseoccurrence timings of a whole slip are early, or conditions whoseoccurrence timings of a whole slip are late are combined with eachother, it is possible to further increase difference in an occurrencetiming of a whole slip.

Thus, in the example illustrated in FIG. 11, a condition of thicknessand a condition of the Young's modulus are combined, and thicknesses ofthe flexible layers 544, 546, 548, and 560 and the Young's modulus areset such that the closer to the center a flexible layer is, the larger athickness thereof is and further the smaller the Young's modulus thereofis. Hence, the larger the Young's modulus is, the earlier an occurrencetiming of a whole slip is, and the smaller a thickness is, the earlieran occurrence timing of a whole slip is, and thus in FIG. 11, the closerto a periphery a flexible layer is, the earlier an occurrence timing ofa whole slip is and the closer to the center of a flexible layer is, thelater an occurrence timing of a whole slip is.

Regarding parameters for making an occurrence timing of a whole slipdifferent, thickness and the Young's modulus are combined, and theperipheral flexible layer 550 whose Young's modulus is large is used forthe heavy object 600 that requires a large gripping force, on the otherhand, the center flexible layer 544 alone whose Young's modulus is smallis used for gripping the light and fragile object 600 that does notrequire a large gripping force. Thus, it is possible to use anappropriate flexible layer in accordance with an object to be gripped.

FIG. 12 is a plan view illustrating a division example that does notdepend on a position in contact with the object 600. In the exampleillustrated in FIG. 12, a flexible layer 552 whose Young's modulus issmall and a flexible layer 554 whose Young's modulus is large are used.As illustrated in the plan view, the flexible layers 552 and theflexible layers 554 are alternately zigzag arranged. In FIG. 12, theflexible layers 552 and 554 having different two respective Young'smoduli are illustrated; however, flexible layers having different threerespective Young's moduli may be arranged. In this case, when flexiblelayers are arranged such that in FIG. 12, Young's moduli of flexiblelayers that are adjacent to each other in a row direction and in acolumn direction are different from each other, zigzag arrangement isobtained even when flexible layers having three or more differentYoung's moduli are arranged. When the flexible layers 552 and 554 havingtwo different respective Young's moduli are arranged, in FIG. 12,flexible layers may be arranged such that Young's moduli of the flexiblelayers on the same row or the same column are the same and the Young'smoduli are different for each row or column.

As described above, the larger the number of division in a region is,the resolution of a sticking rate increases, so that the accuracy ofgripping force control is improved. The larger the number of division ina region is, detection of a sticking rate is able to be executed withrespect to a smaller object and an object having concavity andconvexity. However, the number of division depends on a pitch widthbetween nodes of a distribution pressure sensor, and when the number ofdivision is to be more increased, there presents a limit in terms ofhardware. Thus, as illustrated in FIG. 13, in order to artificiallyreduce a pitch width between nodes of two distribution pressure sensors560 and 562, the distribution pressure sensors 560 and 562 are laminatedin a displaced manner.

In the example illustrated in FIG. 13, from the top, there areillustrated three methods of a case (example (a)) where the twodistribution pressure sensors 560 and 562 are displaced to each other inan alignment direction (x-axis direction) of nodes, a case (example (b))where the two distribution pressure sensors 560 and 562 are displaced toeach other in alignment directions (x-axis direction and y-axisdirection) of nodes, and a case (example (c)) where the distributionpressure sensor 562, which is one of the two distribution pressuresensors, is rotated by 45° and overlapped with the other of the twodistribution pressure sensors.

In the example (a) illustrated in FIG. 13, the distribution pressuresensors 560 and 562 are arranged by displacing them to each other in thex-axis direction by ½ width of a node. In the example (b) illustrated inFIG. 13, the distribution pressure sensors 560 and 562 are arranged bydisplacing them to each other in the x-axis direction and the y-axisdirection by ½ width of a node. The arrangement and the overlappingmethod of the distribution pressure sensors are not limited to theexamples illustrated in FIG. 13.

As described above, when the distribution pressure sensors 560 and 562are arranged by displacing them to each other, it is possible toartificially reduce a pitch width between nodes and to increase thenumber of division in a region.

5.4. Modification 4 (Example in which Flexible Layers are Arranged toInterpose Distribution Pressure Sensor Therebetween)

As described above, as a method for delaying an occurrence timing of awhole slip, there presents a method for increasing a thickness of theflexible layer. On the other hand, when a thickness of a flexible layeris large, there presents a problem that the sensitivity of thedistribution pressure sensor is reduced.

In the modification 4, as illustrated in FIG. 14, a part of a thicknessof a flexible layer 570 arranged upper than a distribution pressuresensor 564 is arranged lower than the distribution pressure sensor 564,and thus the distribution pressure sensor 564 is arranged verticallybetween flexible layers 572 and 574. Movement of a pressure-centerposition depends on a total of thicknesses of the flexible layers 572and 574, on the other hand, detection sensitivity depends on theflexible layer 574 arranged upper than the distribution pressure sensor564, and thus an occurrence timing of a whole slip is able to be delayedwithout reducing detection sensitivity of the distribution pressuresensor 564.

FIG. 15A is a diagram illustrating detection sensitivity by thedistribution pressure sensor 564 in accordance with difference inthickness of a flexible layer. In FIG. 15A, there are illustrateddetection sensitivity (examples (a) to (c)) when three types of theflexible layers 570 having different thickness are arranged on thedistribution pressure sensor 564 and detection sensitivity when thedistribution pressure sensor 564 is arranged vertically between theflexible layers 572 and 574 (modification 4).

In the example (a) illustrated in FIG. 15A, the flexible layer 570having a thickness of 1 mm is arranged on the distribution pressuresensor 564. In the example (b) illustrated in FIG. 15A, the flexiblelayer 570 having a thickness of 3 mm is arranged on the distributionpressure sensor 564, and in the example (c) illustrated in FIG. 15A, theflexible layer 570 having a thickness of 5 mm is arranged on thedistribution pressure sensor 564.

In an example of the modification 4 illustrated in FIG. 15A, theflexible layer 574 having a thickness of 1 mm is arranged on thedistribution pressure sensor 564, and the flexible layer 572 having athickness of 4 mm is arranged under the distribution pressure sensor564.

In FIG. 15A, with respect to the examples (a) to (c) and themodification 4, a pressure detected by the distribution pressure sensor564 and a standard deviation thereof are indicated. As indicated in theexamples (a) to (c), it is found that the larger a thickness of theflexible layer 570 arranged upper than the distribution pressure sensor564 is, the larger a standard deviation of detection values of thepressure is and the more detection sensitivity of the distributionpressure sensor 564 is reduced.

On the other hand, as illustrated in FIG. 15A, in the modification 4,although a total thickness of the flexible layer 572 and the flexiblelayer 574 is the same as that of the example (c), a thickness of theflexible layer 574 arranged upper than the distribution pressure sensor564 is 1 mm, and thus a standard deviation of detection values of thepressure is restrained. Thus, according to the modification 4, detectionsensitivity is able to be obtained, which is similar to that of at leastthe example (a).

FIG. 15B is a characteristic diagram illustrating states of the examples(a) to (c) and the modification 4 that are illustrated in FIG. 15A, inwhich a pressure-center position changes similarly to that of FIG. 3B.As indicated by the examples (a) to (c) illustrated in FIG. 15B, thelarger a thickness of the flexible layer 570 arranged on thedistribution pressure sensor 564 is, the more an occurrence timing of awhole slip delays.

As illustrated in FIG. 15B, an occurrence timing of a whole slip of themodification 4 is a timing similar to that of the example (c).Therefore, according to the modification 4, a thickness of the flexiblelayer 574 arranged upper than the distribution pressure sensor 564 isequalized to that of the flexible layer 570 of the example (a), so thatit is possible to ensure detection sensitivity equivalent to that of theexample (a). Moreover, according to the modification 4, a totalthickness of the flexible layers 572 and 574 vertically between whichthe distribution pressure sensor 564 is interposed is equivalent to thatof the flexible layer 570 of the example (c), so that it is possible toequalize an occurrence timing of a whole slip of the modification 4 tothat of the example (c).

In the feature of the modification 4 illustrated in FIG. 15B, a movingdirection of a pressure-center position is reverse to those of theexamples (a) to (c). This is caused by effects of pressure applied to atop and a bottom of the distribution pressure sensor 564.

FIGS. 16A and 16B are diagrams illustrating a reason that a movingdirection of a pressure-center position of the modification 4 is reverseto those of the examples (a) to (c). In each of FIGS. 16A and 16B, thereare illustrated a state (left part) where the object 600 is not grippedand a state (right part) where the object 600 is gripped, and a statewhere the object 600 is gripped and the corresponding flexible layer isdeformed. In FIGS. 16A and 16B, an arrow A11 indicates a direction inwhich the object 600 is going to slip. Note that, for convenience ofexplanation, illustration of the object 600 is omitted in FIGS. 16A and16B.

FIG. 16A illustrates the example (a), and a state is illustrated inwhich the object 600 is going to slip in a direction of the arrow A11and the flexible layer 570 is deformed in the direction of the arrowA11. In this case, there does not present the flexible layer 570 in aregion A3 illustrated in FIG. 16A and the pressure becomes small, andthus in a pressure detection value of the distribution pressure sensor564, a pressure is small in a left edge and a pressure is large in aright edge of the distribution pressure sensor 564. Thus, as illustratedin FIG. 15B, a pressure-center position moves toward a positivedirection of the x-axis.

On the other hand, the modification 4 is illustrated in FIG. 16B, and astate is illustrated in which the object 600 is going to slip in adirection of the arrow A11 and the flexible layer 572 and the flexiblelayer 574 are deformed in the direction of the arrow A11. In this case,there does not present the flexible layer 572 in a region A4 illustratedin FIG. 16B and the pressure becomes small, and thus in a pressuredetection value of the distribution pressure sensor 564, a pressure issmall in a right edge and a pressure is large in a left edge of thedistribution pressure sensor 564. Thus, as illustrated in FIG. 15B, apressure-center position moves toward a negative direction of thex-axis. In FIG. 15B, a moving direction of a pressure-center position isdifferent from those of the examples (a) to (c) illustrated in FIGS. 3Band 15A; however, a method itself for determining that a whole slipoccurs at a time point when movement of a pressure-center position isstopped is similar to those of the examples (a) to (c) illustrated inFIGS. 3B and 15A.

5.5. Modification 5 (Method for Changing Friction Coefficient ofFlexible Layer)

As a method for changing a friction coefficient a flexible layer, inaddition to a method for changing material, there are considered amethod for micro-fabricating a surface of a flexible layer and a methodfor coating a surface of a flexible layer. Thus, even when a pluralityof flexible layers is made of the same material, various distributionsof friction coefficients are able be generated.

Furthermore, there is exemplified a method for changing a surface areaof a region of each of the flexible layers in order to change thefrictional force of the corresponding flexible layer. The larger asurface area of a flexible layer is, the larger the frictional force is.FIG. 17 is a diagram illustrating an example in which a surface area ofthe flexible layer is changed. An area of a center flexible layer 580 islarger than an area of a peripheral flexible layer 582, and thus thefrictional force of the center flexible layer 580 is larger than thefrictional force of the peripheral flexible layer 582. Thus, it ispossible to make an occurrence timing of a whole slip different betweenthe flexible layer 580 and the flexible layer 582.

Similarly to the modification 4 illustrated in FIG. 14, FIG. 18illustrates an example in which the distribution pressure sensor 564 isarranged vertically between the flexible layers 572 and 574, and furtherillustrates a method for changing the hardness of the flexible layer 572arranged lower than the distribution pressure sensor 564 in order tochange the frictional force of the flexible layer 574 arranged upperthan the distribution pressure sensor 564. In FIG. 18, the hardness ofthe flexible layer 572 arranged lower than the distribution pressuresensor 564 are changed into three types of low (flexible layer 572 a),middle (flexible layer 572 b), and high (flexible layer 572 c).

When change amounts of the flexible layers 572 a to 572 c are constant,the reaction forces Fn generated in the flexible layers 572 a to 572 care different from each other, and thus a distribution of the frictionalforces Ft (=Fn×μ·Fn) generated in flexible layers 574 a to 574 c is ableto be generated. Thus, replacement of a flexible layer in a surface isfacilitated.

5.6. Modification 6 (Example Using Linear Flexible Layer)

In a modification 6, linear flexible layers are arranged instead ofdividing a flexible layer. FIG. 19 is a diagram illustrating aconfiguration example using linear flexible layers 590 and 592 accordingto the modification 6. As illustrated in FIG. 19, the linear flexiblelayers 590 and 592 are arranged on distribution pressure sensors 594 and596. The flexible layer 590 is arranged on the distribution pressuresensor 594, and the flexible layer 592 is arranged on the distributionpressure sensor 596. The flexible layer 592 is made of a material whosefriction coefficient is larger than that of the flexible layer 590.

In FIG. 19, there is illustrated a state where the object 600 is grippedby using the flexible layers 590 and 592. Thus, the object 600 is incontact with the flexible layers 590 and 592 from thereon.

FIG. 19 illustrates chronological movements at a time point t1, a timepoint t2, and a time point t3. The time point t1 indicates a stickingstate. In this state, leading ends of the flexible layers 590 and 592are uniformly directed toward the left.

Next, the time point t2 indicates a state where a partial slip hasoccurred on the object 600. In this state, leading ends of the flexiblelayers 590 whose friction coefficients are small are directed toward theright. On the other hand, leading ends of the flexible layers 592 whosefriction coefficients are large keep a state directed to the left. In acase where a slip has partially occurred, when a direction of theflexible layers 590 that is a slipping regional portion is changed, thepressure of the region becomes small, and thus the distribution pressuresensor 594 is able to detect the change.

Next, the time point t3 indicates a state where a whole slip hasoccurred on the object 600. In this state, the object 600 is slipping inthe right direction, and leading ends of the flexible layers 590 and 592are uniformly directed to the right.

FIG. 20 is a diagram illustrating a configuration of the gripping-forcecalculating unit 200 using the linear flexible layers 590 and 592illustrated in FIG. 19. The pressure acquiring unit 202 acquirespressure detected by the distribution pressure sensors 594 and 596. Thewhole-slip detecting unit 210 monitors change in pressure of the linearflexible layers 590 and 592 so as to detect a slip in each of theflexible layers 590 and 592. As described above, at the time point t2illustrated in FIG. 19, a pressure detection value of the distributionpressure sensor 594 alone which is corresponding to the flexible layer590 is reduced, so that it is possible to detect a state of a partialslip. The sticking-rate calculating unit 212 calculates a rate of anon-detection region of a partial slip to all of the regions. Thegripping-force controlling unit 214 decides a gripping force such that asticking rate calculated by the sticking-rate calculating unit 212 is aconstant value.

When a pressure detection value is reduced, a whole slip is able to bedetected. Change in pressure in each of the linear flexible layers 590and 592, which is acquired by the pressure acquiring unit 202, ismonitored, and when the pressure exceeds a threshold value, a whole slipis detected. The sticking-rate calculating unit 212 calculates a rate ofa non-detection region of a whole slip to all of the regions. In theexample illustrated in FIG. 19, a whole slip occurs in the flexiblelayer 590 alone at the time point t2, and the flexible layer 592 is in asticking state. The total number of the flexible layers 590 and 592 isseven, the number of the flexible layers 592 is four, and thus asticking rate is 57% {=(4/7)×100}.

FIG. 21 is a diagram illustrating an example in which the flexiblelayers 590 and 592 are arranged in multiple directions in theconfiguration using the linear flexible layers 590 and 592 illustratedin FIG. 19. As indicated by the state at the time point t1 illustratedin FIG. 19, in the sticking state, leading ends of the flexible layers590 and 592 are uniformly directed. As illustrated in FIG. 21, whendirections of the flexible layers 590 and 592 in a sticking state arearranged in multiple directions, a configuration capable ofcorresponding to multiple slipping directions is able to be realized.

As described above, according to the present embodiment, a partial slipof an object is able to be detected on the basis of a simpleconfiguration and a simple calculating process alone, and further agripping force of an object is able to be appropriately controlled.Moreover, an occurrence timing of a whole slip is made different in aplurality of flexible layers, so that it is possible to detect a partialslip with high accuracy even under various conditions such as in a caseof a hard object or an object whose surface is plane, and a case wherepressure distribution is flat.

While preferable embodiments of the present disclosure have beendescribed above in detail with reference to the attached drawings, thetechnical scope of the present disclosure is not limited thereto. It isobvious that those skilled in the technical field of the presentdisclosure could have conceived of various changes or modificationswithin the scope of the technical ideas described in the claims, and itis understood that those changes or modifications also reasonably belongto the technical scope of the present disclosure.

For example, in the above-mentioned embodiment, the example is indicatedin which a flexible layer and a distribution pressure sensor areprovided to the hand 500 that grips the object 600; however, the presenttechnology is not limited to the example. For example, the flexiblelayer and the distribution pressure sensor may be arranged on a groundcontact surface of a toe of walking robot so as to detect a slip of thetoe. As described above, the present embodiment may be broadly appliedfor detecting a slip.

The effects described in the present specification are merelyexplanations or exemplifications, and are not limiting. In other words,the techniques according to the present disclosure may exert othereffects that are obvious to those skilled in the art from thedescriptions of the present specification, along with theabove-described effects or instead of the above-described effects.

The present technology may have the following configurations.

(1)

A controller comprising:

a whole-slip detecting unit that detects, based on pressure informationsent from a plurality of regions having different slippingcharacteristics when an object in contact with the plurality of regionsis slipping, a state of a whole slip in which the object is slipping oneach of the plurality of regions.

(2)

The controller according to (1), wherein based on a change in apressure-center position of each of the plurality of regions, thewhole-slip detecting unit detects the state of the whole slip when thecorresponding pressure-center position is a constant value.

(3)

The controller according to (2), wherein

when the pressure-center position becomes the constant value within apredetermined time interval, the whole-slip detecting unit detects thestate of the whole slip.

(4)

The controller according to any one of (1) to (3), wherein

difference between the slipping characteristics of the plurality ofregions makes occurrence timings of whole slips different from eachother.

(5)

The controller according to any one of (1) to (4), wherein

the controller is configured to:

-   -   when detecting the state of the whole slip in at least one of        the plurality of regions and not detecting the state of the        whole slip in others of the plurality of regions, determine a        state of a partial slip in which the object is partially        slipping with respect to the plurality of regions.        (6)

The controller according to (5), wherein

the difference makes occurrence timings of the whole slip in theplurality of regions different, and

the controller is further configured to:

based on difference between the timings, determine the state of thepartial slip.

(7)

The controller according to any one of (1) to (6), wherein

the controller is further configured to:

when not detecting the state of the whole slip in any of the pluralityof regions, determine a sticking state in which the object and theplurality of regions are sticking to each other.

(8)

The controller according to any one of (1) to (7), further comprising:

a sticking-rate calculating unit that calculates a sticking rate betweenthe object and one of the plurality of regions based on a rate of anon-detection region of the state of the whole slip to all of theplurality of regions.

(9)

The controller according to (8), further comprising:

a gripping-force controlling unit that controls, based on the stickingrate, a gripping force in gripping the object by using a gripping unitthat grips the object to which the plurality of regions is provided.

(10)

The controller according to (9), wherein

the gripping-force controlling unit controls the gripping force suchthat the sticking rate is a predetermined value.

(11)

The controller according to (9), further comprising:

an acquisition unit that acquires a rigidity of the object, wherein

the gripping-force controlling unit controls the gripping force based onthe rigidity.

(12)

The controller according to (11), wherein

the gripping-force controlling unit more lowers an increase rate whenincreasing the gripping force, as the rigidity of the object is lower.

(13)

The controller according to any one of (1) to (12), further comprising:

a pressure-gradient calculating unit that calculates a pressure gradientwhen the object is in contact with the plurality of regions; and

a control unit that controls, based on the pressure gradient, a positionin which the plurality of regions is in contact with the object.

(14)

The controller according to (13), wherein

the control unit is configures to:

cause one of the plurality of regions to be in contact with a first partof the object whose pressure gradient is low; and

cause others of the plurality of regions to be in contact with a secondpart of the object whose pressure gradient is higher than the pressuregradient of the first part.

(15)

The controller according to any one of (1) to (14), wherein

the plurality of regions is aligned along a slipping direction of theobject.

(16)

The controller according to any one of (1) to (15), wherein

at least one of a friction coefficient, a Young's modulus, a Poissonratio, a thickness, and a curvature included in the slippingcharacteristics is different for each of the plurality of regions.

(17)

A control method comprising:

based on pressure information sent from a plurality of regions havingdifferent slipping characteristics when an object in contact with theplurality of regions is slipping, detecting a state of a whole slip inwhich the object is slipping on each of the plurality of regions.

(18)

A program allowing a computer to function as:

a means for detecting, based on pressure information sent from aplurality of regions having different slipping characteristics when anobject in contact with the plurality of regions is slipping, a state ofa whole slip in which the object is slipping on each of the plurality ofregions.

REFERENCE SIGNS LIST

-   -   210 Whole-slip detecting unit    -   212 Sticking-rate calculating unit    -   214 Gripping-force controlling unit    -   222 Pressure-gradient calculating unit    -   224 Actuator controlling unit

1. A controller comprising: a whole-slip detecting unit that detects,based on pressure information sent from a plurality of regions havingdifferent slipping characteristics when an object in contact with theplurality of regions is slipping, a state of a whole slip in which theobject is slipping on each of the plurality of regions.
 2. Thecontroller according to claim 1, wherein based on a change in apressure-center position of each of the plurality of regions, thewhole-slip detecting unit detects the state of the whole slip when thecorresponding pressure-center position is a constant value.
 3. Thecontroller according to claim 2, wherein when the pressure-centerposition becomes the constant value within a predetermined timeinterval, the whole-slip detecting unit detects the state of the wholeslip.
 4. The controller according to claim 1, wherein difference betweenthe slipping characteristics of the plurality of regions makesoccurrence timings of whole slips different from each other.
 5. Thecontroller according to claim 1, wherein the controller is configuredto: when detecting the state of the whole slip in at least one of theplurality of regions and not detecting the state of the whole slip inothers of the plurality of regions, determine a state of a partial slipin which the object is partially slipping with respect to the pluralityof regions.
 6. The controller according to claim 5, wherein thedifference makes occurrence timings of the whole slip in the pluralityof regions different, and the controller is further configured to: basedon difference between the timings, determine the state of the partialslip.
 7. The controller according to claim 1, wherein the controller isfurther configured to: when not detecting the state of the whole slip inany of the plurality of regions, determine a sticking state in which theobject and the plurality of regions are sticking to each other.
 8. Thecontroller according to claim 1, further comprising: a sticking-ratecalculating unit that calculates a sticking rate between the object andone of the plurality of regions based on a rate of a non-detectionregion of the state of the whole slip to all of the plurality ofregions.
 9. The controller according to claim 1, further comprising: agripping-force controlling unit that controls, based on the stickingrate, a gripping force in gripping the object by using a gripping unitthat grips the object to which the plurality of regions is provided. 10.The controller according to claim 9, wherein the gripping-forcecontrolling unit controls the gripping force such that the sticking rateis a predetermined value.
 11. The controller according to claim 9,further comprising: an acquisition unit that acquires a rigidity of theobject, wherein the gripping-force controlling unit controls thegripping force based on the rigidity.
 12. The controller according toclaim 11, wherein the gripping-force controlling unit more lowers anincrease rate when increasing the gripping force, as the rigidity of theobject is lower.
 13. The controller according to claim 1, furthercomprising: a pressure-gradient calculating unit that calculates apressure gradient when the object is in contact with the plurality ofregions; and a control unit that controls, based on the pressuregradient, a position in which the plurality of regions is in contactwith the object.
 14. The controller according to claim 13, wherein thecontrol unit is configures to: cause one of the plurality of regions tobe in contact with a first part of the object whose pressure gradient islow; and cause others of the plurality of regions to be in contact witha second part of the object whose pressure gradient is higher than thepressure gradient of the first part.
 15. The controller according toclaim 1, wherein the plurality of regions is aligned along a slippingdirection of the object.
 16. The controller according to claim 1,wherein at least one of a friction coefficient, a Young's modulus, aPoisson ratio, a thickness, and a curvature included in the slippingcharacteristics is different for each of the plurality of regions.
 17. Acontrol method comprising: based on pressure information sent from aplurality of regions having different slipping characteristics when anobject in contact with the plurality of regions is slipping, detecting astate of a whole slip in which the object is slipping on each of theplurality of regions.
 18. A program allowing a computer to function as:a means for detecting, based on pressure information sent from aplurality of regions having different slipping characteristics when anobject in contact with the plurality of regions is slipping, a state ofa whole slip in which the object is slipping on each of the plurality ofregions.